Method of patterning a coating on a substrate

Abstract: In a method in which a top coating (2) on a relatively hard substrate (1) is patterned by means of a stream of kinetic particles while being masked by a mask (3), the substrate (1) is coated with a damping layer (4) before the top coating (2) is provided.

Description: The invention relates to a method of patterning a top coating on a substrate, which top coating is provided on a relatively hard substrate and, while being masked by a mask, is exposed to a stream of kinetic particles. The invention particularly relates to such a method in which the top coating is patterned by means of (powder) spraying. As an alternative to a frequently isotropic etching treatment for patterning the top coating, (powder) spraying is generally quicker and has the additional advantage that the material of the top coating is more directionally taken off so that a sharper and better defined pattern can be obtained. By using a relatively hard substrate as a base, i.e. a substrate which is harder than its top coating and is thus resistant to the stream of kinetic particles, the process automatically stops when the top coating has been removed over its entire thickness and the underlying substrate is reached so that the method should in principle be relatively insensitive to local process fluctuations. Nevertheless, local deviations in the ultimate pattern of the top coating are still found in practice when, for example a conventional (powder) spraying process is used. Particularly, the ultimate pattern appears to be locally attacked at its base and has sometimes even entirely disappeared locally. It is an object of the present invention to provide a method of the type described in the opening paragraph, in which such a breakdown of the top coating pattern is effectively inhibited. The invention is based on the recognition that the local breakdown of the pattern of the top coating is caused by kinetic particles which are scattered on the surface of the relatively hard substrate as soon as they reach the substrate. The particles which are thus substantially scattered non-elastically are reflected towards the base of the pattern and are thus capable of attacking the top coating pattern. To inhibit this phenomenon, a method of the type described in the opening paragraph is characterized in that the substrate is coated with a damping layer before the top coating is provided. A damping layer is understood to mean a layer which is capable of adequately absorbing the kinetic energy of the particles. An embodiment of the method according to the invention, in which the top coating is patterned by means of powder spraying, is characterized in that the substrate is coated with a damping layer of aluminium before the top coating is provided. In practice, the relatively ductile aluminium layer appears to be capable of absorbing the kinetic energy of the powder particles to a sufficient extent so as to neutralize the particles effectively as soon as the top coating has disappeared throughout its thickness. It is thereby avoided that the particles are scattered when they reach the base of the top coating and are reflected towards the (base of) the top coating pattern. In a particular embodiment of the method according to the invention the starting material for the top coating is a bound suspension such as, for example a glass paste which is provided on the damping layer, subsequently cured, at least dried and coated with a photoresist layer from which the mask is formed by selective exposure and development. The rate of erosion of such a cured or dried suspension is generally very large and particularly larger than that of the developed photoresist layer. Thus, a photoresist mask may be used advantageously, which in contrast to a mechanical mask does not need to have an internal coherence and can be very accurately manufactured and aligned by using existing, very sophisticated photolithographic techniques. More particularly, a substrate of glass is used in an embodiment of the method according to the invention and the starting material for the top coating is a glass paste. Thus, an arbitrary glass pattern may be provided on a glass substrate according to the invention. The invention is therefore eminently suitable for use in the manufacture of flat panel picture display devices, in which structured plates, particularly of glass are frequently used. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the drawing Fig. 1 shows a substrate with a top coating which has been patterned by using a conventional powder spraying process; and Figs. 2-3 show successive steps of an embodiment of the method according to the invention, in which a top coating on a substrate is patterned. The Figures are purely diagrammatic and not to scale. For the sake of clarity, some dimensions are exaggerated. In the Figures, corresponding components have been denoted by identical reference numerals as much as possible. The embodiment of Fig. 1 starts from a substrate 1 of glass on which an approximately 180 µm thick top coating 2 of, for example glass paste is provided by means of, for example a silk-screening technique. The top coating 2 is subsequently dried so as to obtain a solid layer of glass grains which are held together by means of a few tenths of percent by weight of a binder. The cured top coating 2 is subsequently provided with a photoresist layer from which a photoresist mask 3 is manufactured by selective exposure and development in the conventional manner. While masking the mask 3, the top coating 2 is exposed to a powder spraying process of aluminium oxide grains. To structure the top coating 2 in a controlled manner, such a low spraying pressure is used that the speed of the spraying particles is low enough to prevent plastic deformation of or cracks in the underlying substrate. After their collision with the substrate, the particles thus still have sufficient energy to be scattered into all directions. Such a substantially non-elastic scattering of particles is presumably the cause of attack of the top coating pattern 2, notably of its base as is shown in Fig. 1. Notably with very fine column or line structures, this attack may in practice have such consequences that the pattern is entirely sprayed off or broken down locally at its base. Figs. 2 and 3 show an embodiment of the method according to the invention. As in the previous embodiment, the starting material is a relatively hard glass substrate 1 provided with an approximately 180 µm thick top coating 2 of a cured glass paste. The same manufacturing steps as in the previous embodiment are used, but in contrast to the previous embodiment the substrate 1 is now coated, in accordance with the present invention, with a damping layer 4 before the top coating 2 is provided. An approximately 2 µm thick aluminium layer is used for the damping layer in this embodiment. While masking a photoresist mask provided in the conventional manner, the assembly is exposed under the same conditions as in the previous embodiment to a powder spraying process 5 of aluminium oxide grains. In this case the energetic grains are taken up by the damping layer 4 when they reach the base of the top coating 2, which damping layer entirely or at least largely absorbs the impact energy of the grains and thus neutralizes them. Consequently, the grains are not reflected or hardly reflected on the substrate so that they cannot attack the pattern of the top coating 2. The ultimate pattern 2 is therefore sharply defined, even in very fine structures, as in this embodiment, with dimensions of 90-170 µm at a pitch of 300-400 µm. At a later stage, the exposed part of the damping layer 4 may be removed, if desired, for example by etching while masking the top coating pattern 2. The invention thus provides a method in which a layer on a relatively hard substrate can be accurately given a predetermined pattern in a controllable manner. Since the invention allows the use of top coatings having a larger rate of erosion than conventional photoresist masks, patterns with and without an internal coherence can be manufactured by means of the method according to the invention. The invention may in principle be used advantageously for any combination of materials. Moreover, instead of aluminium, other materials may be used for the damping layer. As regards the present invention, the damping layer used is only required to be sufficiently ductile so as to absorb the impact energy of the grains completely or substantially completely. Moreover, the invention is also be applicable to processes in which mechanical (steel) masks are used. The invention generally provides a process in which a layer is patterned by means of a stream of kinetic particles, with a better pattern definition and a greater accuracy than comparable existing processes.

Claims: A method of patterning a top coating (2) on a substrate (1), which top coating (2) is provided on a relatively hard substrate (1) and, while being masked by a mask (3), is exposed to a stream of kinetic particles, characterized in that the substrate (1) is coated with a damping layer (4) before the top coating (2) is provided. A method as claimed in Claim 1, in which the top coating (2) is exposed to a powder spraying process, characterized in that the substrate (1) is coated with a damping layer (4) of aluminium before the top coating (2) is provided. A method as claimed in Claim 1 or 2, characterized in that the starting material for the top coating (2) is a bound suspension which is provided on the damping layer (4), subsequently cured, at least dried and coated with a photoresist layer from which the mask (3) is formed by selective exposure and development. A method as claimed in Claim 3, characterized in that a glass paste is used for the top coating (2), in that a layer of aluminium is used for the damping layer (4) and in that the damping layer (4) and the glass paste are consecutively provided on a glass substrate (1).

Inventors: DINGS JACOBUS MARIA, HORNE REMKO, VEEN GERARDUS NICOLAAS ANN VAN, DINGS, JACOBUS MARIA, HORNE, REMKO, VAN VEEN, GERARDUS NICOLAAS ANNE, Dings, Jacobus Maria, c/o Int. Octrooibureau B.V., Horne, Remko, c/o Int. Octrooibureau B.V.
Applicants: PHILIPS ELECTRONICS NV, PHILIPS ELECTRONICS N.V.
Application year: 1994
Main classification: B24C1
IPC codes: G09F9, H01L23, G03F7, H05K3, B24C1